Many factors associated with perforating a well may have an effect on the well productivity. Such factors include gun design including charge type, phasing, shot density, gun types and sizes; charge performance including penetration, hole size, tunnel geometry, gun standoff and eccentricity; conveyance method including tubing conveyed perforating, wireline, extreme overbalance and oriented guns; and reservoir characteristics including permeability, porosity, grain size, compressive strength, unconfined compressive strength, formation fluid type and completion fluid type.
Notwithstanding these numerous parameters, the selection of shaped-charge perforators for use in many completions is based solely on API Section I criteria. API Section I tests are designed to provide a simple means to assess charge penetration performance using standard field guns. The tests are conducted in concrete targets shot under surface conditions then the depth of penetration of the perforations is measured. Consequently, the natural conclusion is to assume that the largest penetration and/or exit hole size delivers the best productivity. Concerns have been raised, however, that charges can be designed to optimize performance in any material, and hence, comparison of performance in concrete targets may be misleading for selecting charges for rocks with different properties under difference conditions.
Accordingly, it would be beneficial to obtain data, such as penetration and inflow performance of given shaped charges, under in-situ conditions. Perforating procedures have been developed to evaluate well perforators under simulated in-situ conditions. For example, API Section IV provides a set of recommended procedures designed to assess performance of perforating gun systems under such conditions. Specifically, the Section IV test is designed to assess perforation inflow performance for a single shaped charge explosive under simulated in-situ stress and perforating conditions. While these procedures have existed since 1985, field validation of experimental results and model predictions based on these procedures have been limited.
Recently, however, a series of tests with Berea and Castlegate sandstone cores under varying in-situ conditions were conducted using these procedures. See “Perforating System Section for Optimum Well Inflow Performance,” Kent Folse, et at. AAPG Annual Convention, May, 2003. In these tests, the sample target is perforated with a single shaped charge under in-situ stress and pore pressure conditions, and then, flowed to simulate well inflow performance. While the results of these experiments have been integrated with theoretical models and field data to improve well productivity for reservoirs in Berea and Castlegate sandstone, similar testing has not been achievable for unconsolidated sandstones due to an inability to simulate the in-situ stress and pore pressure conditions with unconsolidated sandstones. Accordingly, the benefits of Section IV testing and the associated improvements in well performance have not been extended to reservoirs in unconsolidated sandstones.